<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>


    const PI = '3.14';//只读变量
    console.log(PI);

    //x = x + 2;//Uncaught ReferenceError: x is not defined
</script>
</body>
</html>